U.S. patent number 9,960,056 [Application Number 14/430,760] was granted by the patent office on 2018-05-01 for substrate cleaning method, substrate cleaning apparatus and vacuum processing system.
This patent grant is currently assigned to TOKYO ELECTRON LIMITED. The grantee listed for this patent is Tokyo Electron Limited. Invention is credited to Kazuya Dobashi, Kensuke Inai, Misako Saito.
United States Patent |
9,960,056 |
Dobashi , et al. |
May 1, 2018 |
Substrate cleaning method, substrate cleaning apparatus and vacuum
processing system
Abstract
In order to remove a deposit adhered to the backside of the
peripheral portion of a wafer, a cleaning gas containing carbon
dioxide gas is set to a pressure that is slightly lower than the
pressure corresponding to a vapor pressure line of carbon dioxide
at a temperature in the nozzle, and a gas cluster of carbon dioxide
is generated. A gas cluster of carbon dioxide generated under such
a condition is in a state immediately prior to undergoing a phase
change to a liquid and therefore is a gas cluster having a large
cluster diameter and having molecules that are firmly
solidified.
Inventors: |
Dobashi; Kazuya (Nirasaki,
JP), Inai; Kensuke (Nirasaki, JP), Saito;
Misako (Nirasaki, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Tokyo Electron Limited |
Tokyo |
N/A |
JP |
|
|
Assignee: |
TOKYO ELECTRON LIMITED (Tokyo,
JP)
|
Family
ID: |
50387408 |
Appl.
No.: |
14/430,760 |
Filed: |
August 28, 2013 |
PCT
Filed: |
August 28, 2013 |
PCT No.: |
PCT/JP2013/005079 |
371(c)(1),(2),(4) Date: |
March 24, 2015 |
PCT
Pub. No.: |
WO2014/049959 |
PCT
Pub. Date: |
April 03, 2014 |
Prior Publication Data
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|
|
Document
Identifier |
Publication Date |
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US 20150255316 A1 |
Sep 10, 2015 |
|
Foreign Application Priority Data
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|
|
|
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Sep 28, 2012 [JP] |
|
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2012-217539 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B08B
5/02 (20130101); H01L 21/0209 (20130101); H01L
21/02087 (20130101); H01L 21/67028 (20130101); B08B
13/00 (20130101); H01L 21/67051 (20130101) |
Current International
Class: |
H01L
21/67 (20060101); B08B 13/00 (20060101); H01L
21/02 (20060101); B08B 5/02 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
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2007-232901 |
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Sep 2007 |
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JP |
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2011-171584 |
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Sep 2011 |
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JP |
|
2012-119065 |
|
Jun 2012 |
|
JP |
|
10-2012-0030000 |
|
Mar 2012 |
|
KR |
|
2010/021265 |
|
Feb 2010 |
|
WO |
|
2011/115155 |
|
Sep 2011 |
|
WO |
|
WO 2011115157 |
|
Sep 2011 |
|
WO |
|
Other References
English Machine Translation of JP 2011-171584. cited by examiner
.
English Machine Translation of WO 2011-115157. cited by examiner
.
The International Search Report dated Nov. 26, 2013. cited by
applicant.
|
Primary Examiner: Blan; Nicole
Claims
What is claimed is:
1. A substrate cleaning method for removing a deposit adhered to a
backside or a peripheral portion of a substrate, the substrate
cleaning method comprising: supporting a substrate by a support;
adjusting and maintaining a pressure in a processing chamber to be
a vacuum atmosphere; adjusting and maintaining a pressure inside a
nozzle unit to be higher than the pressure in the processing
chamber; and ejecting a cleaning gas containing a carbon dioxide
gas to the backside or the peripheral portion of the substrate from
the nozzle unit as an aggregate of atoms or molecules of carbon
dioxide gas through adiabatic expansion to remove the deposit from
the backside or the peripheral portion of the substrate, wherein
the pressure inside the nozzle unit is set to be slightly lower
than a pressure on a vapor pressure line of carbon dioxide at a
temperature of the cleaning gas in the nozzle unit, so that a gas
cluster is generated in a solidified state, and wherein the
pressure inside the nozzle unit is higher than or equal to 75% and
lower than 100% of the pressure on the vapor pressure line of
carbon dioxide.
2. The substrate cleaning method of claim 1, wherein the cleaning
gas further contains helium gas.
3. The substrate cleaning method of claim 2, wherein a flow rate of
the helium gas is greater than that of the carbon dioxide gas.
4. The substrate cleaning method of claim 3, wherein a flow rate
ratio of the carbon dioxide gas to the helium gas is 1:9.
5. The substrate cleaning method of claim 1 further comprising:
supplying a purge gas from a side of a top surface of the substrate
to the top surface of the substrate when ejecting the gas cluster
to the backside or the peripheral portion of the substrate.
6. The substrate cleaning method of claim 1, wherein removing the
deposit by ejecting the gas cluster to the backside or the
peripheral portion of the substrate is performed in a state where a
shield member is provided at a position shifted toward a center
from an outer periphery on a top surface of the substrate while
being separated from the substrate with a gap to suppress adhesion
of the deposit peeled from the substrate to the top surface of the
substrate.
7. The substrate cleaning method of claim 1, wherein the substrate
has a circular shape and the gas cluster is ejected to the backside
or the peripheral portion of the substrate during rotation of the
support.
8. A substrate cleaning apparatus comprising: a support disposed in
a processing chamber having a gas exhaust port and configured to
support a substrate; a nozzle unit configured to eject a gas
cluster to a backside or a peripheral portion of the substrate to
remove a deposit adhered to the backside or the peripheral portion
of the substrate being supported by the support; a gas supply unit
configured to supply a cleaning gas containing carbon dioxide gas
to the nozzle unit; a pressure controller configured to control a
pressure in the nozzle unit; a moving mechanism configured to
relatively move the nozzle unit and the support, and a control unit
programmed to control the pressure controller and configured to:
set a pressure in the processing chamber to be a vacuum atmosphere;
and set a pressure inside the nozzle unit to be (1) slightly lower
than a pressure on a vapor pressure line of carbon dioxide at a
temperature of the cleaning gas in the nozzle unit and (2) higher
than or equal to 75% and lower than 100% of the pressure on the
vapor pressure line of carbon dioxide to generate the gas cluster
in a solidified state.
9. The substrate cleaning apparatus of claim 8, wherein the
cleaning gas further contains helium gas.
10. The substrate cleaning apparatus of claim 9, wherein a flow
rate of the helium gas is greater than that of the carbon dioxide
gas.
11. The substrate cleaning apparatus of claim 10, wherein a flow
rate ratio of the carbon dioxide gas to the helium gas is 1:9.
12. The substrate cleaning apparatus of claim 8, further comprising
a purge gas supply unit configured to supply a purge gas from a
side of a top surface of the substrate to the top surface of the
substrate when the gas cluster is ejected to the backside or the
peripheral portion of the substrate.
13. The substrate cleaning apparatus of claim 8, further comprising
a shielding member disposed at a position shifted toward a center
from an outer periphery on a top surface of the substrate while
being separated from the substrate with a gap to suppress adhesion
of the deposit peeled from the substrate to the top surface of the
substrate.
14. The substrate cleaning apparatus of claim 8, wherein substrate
has a circular shape, and further comprising a rotation unit to
rotate the substrate about a center of the substrate by the
support.
15. A vacuum processing system comprising: a vacuum transfer
chamber configured to transfer a substrate under a vacuum
atmosphere; a vacuum processing module coupled to the vacuum
transfer chamber through a partition valve and configured to
perform vacuum processing on the substrate, the vacuum processing
module being an etching apparatus or a film forming apparatus; and
the substrate cleaning apparatus of claim 8 coupled to the vacuum
transfer chamber through a partition valve and configured to clean
at least one of the backside and the peripheral portion of the
substrate that has been subject to the vacuum processing in the
vacuum processing module.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a national stage application of PCT Application
No. PCT/JP2013/005079, filed on Aug. 28, 2013, and claims priority
to and benefit of the Japanese Patent Application No. 2012-217539,
filed on Sep. 28, 2012. The entire contents of the foregoing patent
applications are incorporated herein by reference in entirety.
FIELD OF THE INVENTION
The present invention relates to a technique for cleaning a
peripheral portion or a backside of a substrate.
BACKGROUND OF THE INVENTION
In a semiconductor device manufacturing process, there has been
known a process of forming a hole or a trench in a multilayer film
formed on a semiconductor wafer (hereinafter, referred to as
"wafer") through a resist mask formed on the multilayer film by an
etching gas suitable for each film by using a single etching
apparatus. However, a deposit may be deposited to a peripheral
portion or a backside of the wafer during the above process. This
is because an etching residue is adhered to the wafer in a dry
etching process and a film forming gas flows toward the backside of
the wafer in a film forming process. The deposit may cause
particles when the wafer is transferred or processed in a next
process. Therefore, the deposit needs to be removed. As for a
method for cleaning a deposit firmly adhered to the peripheral
portion of the wafer, brush cleaning using a resin material, CMP
(Chemical Mechanical Polishing) or the like has been conventionally
used. However, such a method is mechanical and may cause secondary
contamination from the cleaning members. Further, water is used for
the cleaning, so that an adverse effect from water may be caused.
In other words, if a thin film on the wafer is made of a soluble
material, elution may occur or a low dielectric film such as SiCOH
or the like may be damaged.
International Publication No. 2010/021265 discloses a technique for
etching or planarizing a semiconductor substrate or a thin film
layer on a surface of the semiconductor substrate by ejecting a gas
cluster to the semiconductor substrate without ionizing the gas
cluster. However, a technique for cleaning a peripheral portion of
a wafer is not disclosed therein.
Further, Japanese Patent Application Publication No. 2007-232901
discloses a technique for removing a photoresist film by ejecting
particles of dry ice toward a wafer. However, when the particles of
the dry ice are ejected to the wafer to remove a polymer adhered to
the wafer W, the wafer may be broken or secondary contamination
from the dry ice may occur.
SUMMARY OF THE INVENTION
In view of the above, the present invention provides a technique
capable of cleaning a deposit adhered to a peripheral portion or a
backside of a substrate while suppressing adverse effect on the
substrate.
In accordance with an aspect of the present invention, there is
provided a substrate cleaning method for removing a deposit adhered
to a backside or a peripheral portion of a substrate. The substrate
cleaning method includes: supporting a substrate by a support;
generating a gas cluster as an aggregate of atoms or molecules of
carbon dioxide gas by adiabatic expansion, by ejecting a cleaning
gas containing the carbon dioxide gas to a processing atmosphere
from a nozzle unit in which a pressure is set to be higher than a
pressure of the processing atmosphere where a substrate is
provided; and removing the deposit by ejecting the gas cluster to
the backside or the peripheral portion of the substrate. The
pressure inside the nozzle unit is set to a pressure slightly lower
than a pressure on a vapor pressure line of carbon dioxide at a
temperature of the cleaning gas in the nozzle unit, at which a firm
gas cluster of the carbon dioxide gas is generated.
In accordance with another aspect of the present invention, there
is provided a substrate cleaning apparatus including: a support
provided in a processing chamber having a gas exhaust port to
support a substrate; a nozzle unit configured to eject a gas
cluster to a backside or a peripheral portion of the substrate to
remove a deposit adhered to the backside or the peripheral portion
of the substrate supported by the support; a gas supply unit
configured to supply a cleaning gas containing carbon dioxide gas
to the nozzle unit; a pressure controller configured to control a
pressure in the nozzle unit; and a moving mechanism configured to
relatively move the nozzle unit and the support. A pressure inside
the nozzle unit is set to a pressure slightly lower than a pressure
on a vapor pressure line of carbon dioxide at a temperature of the
cleaning gas in the nozzle unit, at which a firm gas cluster of the
carbon dioxide is generated.
In accordance with still another aspect of the present invention,
there is provided a vacuum processing system including: a vacuum
transfer chamber configured to transfer a substrate under a vacuum
atmosphere; a vacuum processing module connected to the vacuum
transfer chamber through a partition valve and configured to
perform vacuum processing on the substrate; and the substrate
cleaning apparatus connected to the vacuum transfer chamber through
a partition valve and configured to clean at least one of the
backside and the peripheral portion of the substrate that has been
subjected to the vacuum processing in the vacuum processing
module.
EFFECT OF THE INVENTION
The present invention generates a gas cluster of carbon dioxide
(aggregate of carbon dioxide molecules) by setting a cleaning gas
containing carbon dioxide gas to a pressure slightly lower than a
pressure on a vapor pressure line of carbon dioxide at a
temperature in the nozzle unit. The gas cluster of carbon dioxide
generated under such a condition is in a state immediately prior to
undergoing a phase change to a liquid. Therefore, the gas cluster
has a large cluster diameter (the number of molecules forming the
cluster is large) and contains molecules that are firmly
solidified. Accordingly, when the gas cluster is ejected to a
peripheral portion or a backside of the substrate, a strong
cleaning force is exerted. As a result, it is possible to
effectively remove a deposit and perform the cleaning locally,
which prevents the surface of the substrate (surface to be
processed on which a desired process for forming an integrated
circuit or the like is performed) from being damaged.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows an arrangement for a cleaning method in accordance
with an embodiment of the present invention.
FIG. 2 is a graph describing the characteristics of a gas-liquid
boundary curve of carbon dioxide.
FIG. 3 is an explanatory view showing a process of removing a
deposit from a peripheral portion of a substrate by a gas
cluster.
FIG. 4 is an explanatory view showing a process of removing the
deposit from the peripheral portion of the substrate by the gas
cluster.
FIG. 5 shows an arrangement for a cleaning method in accordance
with another embodiment of the present invention.
FIG. 6 is a top view showing an entire vacuum processing system in
accordance with an embodiment of the present invention.
FIG. 7 is a vertical cross sectional side view showing a substrate
cleaning apparatus in accordance with a first embodiment of the
present invention.
FIG. 8 is a top view showing the substrate cleaning apparatus in
accordance with the first embodiment of the present invention.
FIG. 9 is a vertical cross sectional side view showing a nozzle
unit used for the substrate cleaning apparatus.
FIG. 10 is a vertical cross sectional side view showing a substrate
cleaning apparatus in accordance with a second embodiment of the
present invention.
FIG. 11 is a top view showing a shielding plate in accordance with
the second embodiment of the present invention.
FIG. 12 is an explanatory view showing a structure for preventing
re-adhesion of the deposit removed by the gas cluster.
FIG. 13 is a perspective view showing a polysilicon pattern formed
on a bare silicon wafer.
FIG. 14 is an SEM image showing a state obtained when the gas
cluster is ejected to the polysilicon pattern in a test
example.
FIG. 15 is an SEM image showing a state obtained when the gas
cluster is ejected to the polysilicon pattern in the test
example.
FIG. 16 is an SEM image showing a state obtained when the gas
cluster is ejected to the polysilicon pattern in the test
example.
FIG. 17 is a graph showing the characteristics of relation between
a pressure of CO.sub.2 gas and a tilt ratio of a mask pattern.
FIG. 18 is an SEM image showing an effect of ejection of the gas
cluster to a wafer in the test example.
DETAILED DESCRIPTION OF THE EMBODIMENTS
A substrate processing method in accordance with the present
invention is a method for generating a gas cluster by converting
carbon dioxide (CO.sub.2) into a cluster, ejecting the generated
gas cluster to a peripheral portion or a backside of a substrate to
remove a deposit therefrom.
Hereinafter, a gas cluster generation process will be described.
First, CO.sub.2 gas is compressed at a pressure of a few MPa, e.g.,
about 5 MPa. The gas in a high-pressure state is discharged to a
vacuum atmosphere through, e.g., an orifice. The discharged
CO.sub.2 gas is expanded at once, so that a temperature thereof
becomes lower than a condensation temperature by the adiabatic
expansion. The condensed molecules are bonded by a Van der Waals
force. As a result, a gas cluster that is an aggregate of CO.sub.2
molecules is generated. CO.sub.2 gas is used for the following
reasons. CO.sub.2 gas has a specific heat ratio .gamma. of about
1.29 and Ar has a specific heat ratio .gamma. of about 1.67, for
example. Kinetic energy K per a single molecule of a gas cluster is
expressed by an equation
K=.gamma./(.gamma.-1).times.K.sub.B.times.T.sub.0. K.sub.B
represents a voltzmann constant and T.sub.0 represents a gas
temperature.
From the above equation, when the gas temperature is 27.degree. C.,
the kinetic energy per a single molecule of CO.sub.2 becomes 115
meV and the kinetic energy per a single molecule of Ar becomes 64.6
meV. Since CO.sub.2 gas has a higher kinetic energy per a single
molecule, a gas cluster having a higher physical energy can be
generated. A pressure in the nozzle unit 6 (a primary pressure of
an orifice as an injection opening of the nozzle unit 6) for
generating a gas cluster, i.e., a pressure before CO.sub.2 gas is
adiabatically expanded, is slightly lower than a pressure on a
vapor pressure line (gas-liquid boundary line) at a temperature of
the CO.sub.2 gas. At such a pressure, a firm gas cluster is
obtained. This pressure will be defined later.
FIG. 1 shows an embodiment in accordance with the present
invention. In the substrate cleaning method of the present
invention, there is employed a rotating stage 42 serving as a
support for supporting a wafer W, for example. The rotating stage
42 is configured as, e.g., an electrostatic chuck, and supports the
wafer W horizontally while attracting a central portion of a
backside of the wafer W. A nozzle unit 6 for generating a cluster
is provided at a position corresponding to the backside of the
wafer W on the rotating stage 42. The nozzle unit 6 includes a
cylindrical pressure chamber 67. The injection opening 66 is formed
at a leading end portion of the nozzle unit 6.
An orifice is formed at a base end portion of the injection opening
66. The injection opening 66 is widened toward the leading end
portion in a trumpet shape. A gas supply line 50 that is a pipe is
connected to a base end side of the nozzle unit 6. The gas supply
line 50 is connected to a CO.sub.2 gas supply source 51 and
constitutes a gas supply unit. The gas supply unit includes the
CO.sub.2 gas supply source 51, a flow rate controller 52, a valve
53, a booster 54, a pressure gauge 55 and a valve 56 which are
installed from an upstream side. These components constitute a
cleaning gas supply system 8. A pressure in the pressure chamber 67
is controlled by controlling a flow rate of CO.sub.2 gas supplied
from the CO.sub.2 gas supply source 51 by the flow rate controller
52 based on a detection value of the pressure guage 55.
Hereinafter, a pressure of CO.sub.2 for generating a gas cluster
will be described with reference to FIG. 2. FIG. 2 shows a vapor
pressure line (gas-liquid boundary line) of CO.sub.2. CO.sub.2 is
in a liquid state at an upper region of the vapor pressure line and
in a gaseous state at a lower region of the vapor pressure line. A
supercritical state of CO.sub.2 occurs at a region where a pressure
is 7.38 MPa or above and a temperature is 31.1.degree. C. or above.
A triple point occurs at a pressure of 0.52 MPa and a temperature
of -56.6.degree. C. A pressure of CO.sub.2 gas on a primary side of
an orifice of the present invention is set to a pressure slightly
lower than a pressure on the vapor pressure line at a temperature
of the CO.sub.2 gas, i.e., a pressure at which a firm gas cluster
is obtained. The CO.sub.2 gas that is set to such a pressure is in
a state immediately prior to undergoing a phase change from gas to
liquid. Therefore, the gas cluster of CO.sub.2 has a large cluster
diameter (the number of molecules forming the cluster is large) and
contains molecule that are firmly solidified. Accordingly, the gas
cluster can apply strong impact to a target object.
A firm gas cluster of CO.sub.2 can collapse a rectangular
polysilicon pattern having a height of 100 nm, a width of 45 nm and
a length of 600 nm, which is formed on a surface of a bare silicon
wafer, for example. On the other hand, a gas cluster of CO.sub.2
generated at a pressure much lower than the pressure on the vapor
pressure line, e.g., by 25% or more cannot collapse the
pattern.
In a test example to be described later, relation between a
pressure and presence or absence of pattern collapse was obtained
by ejecting a gas cluster to an actual pattern group while varying
a pressure in the nozzle unit 6. It is possible to clearly
determine from the result whether or not a gas cluster is firm. In
other words, as can be seen from the presence or the absence of the
pattern collapse, a firm gas cluster and a gas cluster that is
generated at a pressure considerably lower than the pressure on the
vapor pressure line and cannot be said to be firm have different
impact forces and thus have considerably different cleaning
capability. This indicates that the pressure slightly lower than
the pressure on the vapor pressure line at the temperature of
CO.sub.2 gas, i.e., the pressure at which a firm gas cluster is
obtained, can be clearly distinguished from a pressure lower than a
minimum level of the pressure at which a firm gas cluster is
obtained by ejecting each gas cluster to, e.g., a pattern or the
like. Thus, the pressure slightly lower than the pressure on the
vapor pressure line can be clearly determined.
Specifically, the pressure slightly lower than the pressure on the
vapor pressure line is higher than at least 75% of the pressure on
the vapor pressure line. In such a pressure range, a firm gas
cluster is generated. In FIG. 2, the range of "the slightly lower
pressure" is illustrated as a shaded region.
As shown in FIG. 3, the gas cluster thus generated is ejected from
the nozzle unit 6 in an axis direction of the nozzle unit 6 and
collides with the deposit 10 adhered to the peripheral portion of
the wafer W at an inclined angle of about 45.degree., for example,
with respect to the surface of the wafer W. Accordingly, as shown
in FIG. 4, the gas cluster 3 is decomposed to individual CO.sub.2
molecules and the deposit 10 is broken and peeled by the impacts of
the collision of the gas cluster 3 and the scattering of the
CO.sub.2 molecules. The peeled deposit scatters toward the outer
side of the wafer and also toward the space above the wafer W.
Therefore, it is preferable to supply a purge gas to the surface of
the wafer W as will be described in a following specific example.
Further, a shielding plate may be provided as will be described in
the following specific example. A reference numeral 30 in FIG. 3
indicates CO.sub.2 molecules before clustering.
In the substrate cleaning apparatus of the present invention, a gas
cluster may be generated by supplying He gas in addition to
CO.sub.2 gas to the nozzle unit 6. For example, as shown in FIG. 5,
the pipe of the gas supply line 50 is branched at an upstream side
of the booster 54 to be connected to a He supply source 91 through
a branch line 94. A flow rate controller 92 and a valve 93 are
provided at the branch line 94 from the upstream side thereof. A
branch line 95 serves as a branch line for CO.sub.2 gas. A mixing
ratio of CO.sub.2 gas and He gas may be controlled by the flow rate
controllers 52 and 92 to, e.g., 1:9. In that case, a pressure in
the nozzle unit 6 is set to a pressure slightly lower than the
pressure on the vapor pressure line, e.g., 5 MPa, at 20.degree. C.
In the case of generating a gas cluster by using CO.sub.2 gas mixed
with He gas, the ejection speed of the gas cluster can be increased
and, thus, a high-energy gas cluster can be obtained, which is
preferable.
(First Embodiment)
Next, an example of a specific apparatus for implementing the
above-described substrate cleaning method will be described. FIG. 6
shows a vacuum processing system having a substrate cleaning
apparatus 4 in accordance with the embodiment of the present
invention. The vacuum processing system includes an atmospheric
transfer chamber 1 having a rectangular shape when seen from the
top. A loading/unloading port for loading/unloading a wafer W is
provided at one longitudinal side of the atmospheric transfer
chamber 1. The loading/unloading port has a plurality of
loading/unloading stages 13, on each of which a FOUP as a transfer
container that accommodates a plurality of wafers W is mounted, and
a door 14 provided at each of the loading/unloading stage 13.
A vacuum transfer chamber 2 having, e.g., a hexagonal shape when
seen from the top, is connected to a side of the atmospheric
transfer chamber 1 which is opposite to the side where the
loading/unloading stages 13 are provided through a right and a left
load-lock chamber 15 (preliminary vacuum chambers). An alignment
module 16 having an orienter for adjusting the orientation of the
wafer W is connected to a short side of the atmospheric transfer
chamber 1. Provided in the atmospheric transfer chamber 1 is a
transfer unit 12 for transferring the wafer W among the
loading/unloading stages 13, the load-lock chambers 15 and the
alignment module 16.
The vacuum transfer chamber 2 is maintained in a vacuum atmosphere
by a vacuum pump (not shown). The vacuum transfer chamber 2 is
connected to a first vacuum chamber 31 of an etching apparatus in
which an etching atmosphere is formed and a second vacuum chamber
41 of a substrate cleaning apparatus 4 in which a cleaning
atmosphere is formed. Provided in the vacuum transfer chamber 2 is
a transfer mechanism 22 for transferring the wafer W among the
load-lock chambers 15, the alignment module 16, the etching
apparatus and the substrate cleaning apparatus 4. Notations G1 to
G3 in FIG. 6 represent gate valves serving as partition valves.
The vacuum processing system includes a control unit 9. The
transfer of the wafer W, the opening/closing of the gate valves G1
to G3 and the doors 14, the processing and the vacuum level in the
vacuum chambers 31 and 41 are controlled by software including a
processing recipe and a program stored in a storage unit of the
control unit 9.
As for the etching apparatus, a known apparatus of a capacitively
coupled plasma type, an induction coil plasma type or the like can
be used. In the capacitively coupled plasma etching apparatus, an
upper electrode and a lower electrode are provided to be opposite
to each other in the vacuum chamber 31 and a processing gas is
converted into a plasma by applying a high frequency power between
both electrodes. The surface of the wafer W is etched by attracting
ions in the plasma to the wafer W on the lower electrode by a bias
power applied to the lower electrode.
As shown in FIGS. 7 and 8, the substrate cleaning apparatus 4
including the second vacuum chamber 41 in which a processing
atmosphere is formed has the rotating stage 42 including an
electrostatic chuck for supporting the wafer W horizontally. The
rotating stage 42 is supported by a rotation unit 44 as a moving
unit fixed to the bottom portion of the second vacuum chamber 41
through a rotation shaft 43. The rotating stage 42 can rotate the
wafer W attracted and held thereon about a vertical axis.
A guide rail 61 extending in a horizontal direction (X direction)
is provided at the bottom surface of the second vacuum chamber 41.
A moving body 62 is driven by a ball screw mechanism (not shown)
while being guided by the guide 61. As shown in FIG. 9, a
supporting member 63 is provided on the moving body 62 to extend
vertically upward (Z direction in the drawing) and then extend in a
Y direction in the drawing. A nozzle unit 6 (referred to as "first
nozzle unit 6" in this example) connected to the cleaning gas
supply system 8 shown in FIG. 1 is provided at a leading end
portion of the supporting member 63 through an angle adjusting unit
64.
The first nozzle unit 6 is provided at a position for ejecting a
gas cluster to the peripheral portion of the backside of the wafer
W held by the rotating stage 42. The angle adjusting unit 64 is
configured as a driving unit including a motor having a rotation
shaft 65 extending in the Y direction. The first nozzle unit 6
having a main body fixed to the leading end of the rotation shaft
65 so that an ejection angle of a gas cluster can be controlled by
rotating the rotation shaft 65 by the angle adjusting unit 64.
Further, a second nozzle unit 90 having the same configuration as
the first nozzle unit 6 is provided above the wafer W. The second
nozzle unit 90 is configured to eject a gas cluster to an edge
portion of the wafer W from above in a vertical direction. Further,
the second nozzle unit 90 is connected to a moving body 87 through
a supporting member 88. The moving body 87 is fixed to a guide rail
86 provided at the bottom portion of the second vacuum chamber 41
and horizontally movable in the X direction along the guide rail
86. The second nozzle unit 90 is connected to a pipe branched from
the cleaning gas supply system 8 and extending in parallel
thereto.
As shown in FIG. 7, a purge gas nozzle 80 is provided above the
wafer W in the second vacuum chamber 41. The purge gas nozzle 80 is
configured to form a flow of a purge gas, e.g., Ar gas, nitrogen
gas or the like, at the peripheral portion of the top surface of
the wafer W. The purge gas nozzle 80 is connected to a supporting
member 83 and a moving body 82 having the same configurations as
those of the nozzle unit 6. The moving body 82 is fixed to a guide
rail 81 provided at the bottom portion of the second vacuum chamber
41 and horizontally movable in the X direction along the guide rail
81. The purge gas nozzle 80 is connected to a purge gas supply
system 85 provided at the outside of the second vacuum chamber 41.
The purge gas supply system 85 includes, e.g., a purge gas supply
source, a flow rate controller, a valve or the like.
A gas exhaust pipe 49 is connected to a gas exhaust port 45 formed
at the bottom portion of the second vacuum chamber 41. A vacuum
pump 47 is connected to the gas exhaust pipe 49 via a pressure
control unit 46, so that a pressure in the second vacuum chamber 41
can be controlled.
Hereinafter, an operation of the vacuum processing system will be
described. First, a transfer container, e.g., a FOUP, accommodating
therein wafers W is mounted on the loading/unloading stage 13 and
the door 14 opens together with a lid of the transfer container.
Next, a wafer W in the transfer container is transferred by the
transfer unit 12 in the atmospheric transfer chamber 1 to the
alignment module 16 and an orientation of the wafer W is adjusted
to a preset orientation. Then, the wafer W is loaded into the first
vacuum chamber 31 of the etching apparatus via the transfer unit
12, the load-lock chamber 15, and the transfer mechanism 22 in the
vacuum transfer chamber 2.
The wafer W has an organic film, for example, formed thereon and a
resist mask formed on the organic film. At the peripheral portion
of the wafer W, the resist and the organic film are removed and
silicon that is a base of the wafer W is exposed. In the etching
apparatus, a recess is formed in a pattern corresponding to the
pattern of the resist mask by etching the organic film by a plasma.
A deposit that is a reaction by-product or the like generated by
the etching is adhered to a beveled portion (peripheral portion) of
the backside of the etched wafer W.
Thereafter, the wafer W is loaded into the second vacuum chamber 41
of the substrate cleaning apparatus 4 and rotated by the rotation
unit 44 while being attracted and held on the rotating stage 42. A
pressure in the second vacuum chamber 41 is maintained in a vacuum
atmosphere of, e.g., 1 Pa to 500 Pa, by the pressure control unit
46 and, also, the pressure in the nozzle unit 6 is set to the
above-described level. Next, the deposit is removed by ejecting the
gas cluster from the nozzle unit 6. As described above, the deposit
is separated from the wafer W by the physical impact of the gas
cluster of CO.sub.2. The separated deposit (reaction by-product)
scatters to the outer side of the wafer W by the suction of the
vacuum pump 47 and the purge gas ejected from the purge gas nozzle
80 toward the peripheral portion of the surface of the wafer W. The
scattered deposit flows toward a position below the wafer W and is
discharged to the outside of the second vacuum chamber 41 through
the gas exhaust port 45. In this manner, the deposit is removed
from the peripheral portion of the wafer W. Upon completion of the
cleaning of the peripheral portion of the wafer W, the gate valve
G3 is opened and the wafer W is unloaded from the second vacuum
chamber 41 by the transfer mechanism 22 of the vacuum transfer
chamber 2.
In the above embodiment, a firm CO.sub.2 cluster is obtained by
controlling a pressure of CO.sub.2 gas in the nozzle unit 6 to a
pressure slightly lower than a pressure on a vapor pressure line at
a temperature in the nozzle unit 6 and the gas cluster thus
obtained is ejected to the peripheral portion of the wafer W.
Hence, the deposit adhered to the peripheral portion of the wafer W
can be reliably removed. Accordingly, the peripheral portion of the
wafer W can be effectively cleaned.
In the substrate cleaning apparatus shown in FIG. 7, CO.sub.2 gas
is supplied to the nozzle unit 6. However, as described with
reference to FIG. 5, a gaseous mixture of CO.sub.2 gas and He gas
may be supplied to the nozzle unit 6. Further, the deposit to be
cleaned by the gas cluster is not limited to the deposit adhered to
the peripheral portion of the wafer W and may also be a deposit
adhered to the backside of the wafer W. The deposit adhered to the
backside of the wafer W may include a deposit transferred from the
electrostatic chuck during the contact with the electrostatic chuck
or a film (deposit) formed on the backside of the wafer W by a film
forming gas flowing into the space between the wafer W and the
electrostatic chuck supporting the backside of the wafer W during
film formation on the wafer W.
The vacuum processing system in accordance with the present
invention is not limited to the etching apparatus and may also be
an apparatus including a vacuum processing apparatus (vacuum
processing module) such as a film forming apparatus or the
like.
The substrate to be processed is not limited to a circular
substrate such as a wafer W and may also be a polygonal substrate,
e.g., a substrate for use in flat panel display (FPD) or the like.
In this case, the substrate cleaning process can be performed by
relatively moving the nozzle units 6 and 90 and the purge gas
nozzle 80 with respect to the substrate from one end to the other
end along the periphery thereof.
(Second Embodiment)
As shown in FIGS. 10 and 11, a shielding plate 89 as a shielding
member is provided at a side of the surface of a wafer W to prevent
a broken deposit from adhering to the surface of the wafer W. The
shielding plate 89 is a vertically standing plate and has an arc
shape curved along the peripheral portion of the wafer W when seen
from the top. The shielding plate 89 is provided at a position
shifted toward the center from the outer periphery (outermost line
of the peripheral portion) of the wafer W mounted on the rotating
stage 42 along the peripheral portion thereof. The wafer W is
located at a height position (processing position) with a gap from
the shilding plate 89 during the cleaning using a gas cluster. The
shielding plate 89 is configured to be vertically movable by an
elevation unit 95 provided in the second vacuum chamber 41 through
a supporting arm 96, between the processing position and a retreat
position where the shielding plate 89 does not interfere with the
transfer unit in the second processing chamber 41 during the
transfer of the wafer W.
Next, an operation in accordance with the second embodiment will be
described. FIG. 12 shows scattering of deposits in the case of
ejecting a gas cluster from the first nozzle unit 6 provided below
the wafer W. For example, in the case of ejecting a gas cluster to
a wafer W at an angle of 45.degree. with respect to the backside of
the wafer W, the deposits 10 are broken by the gas cluster 3 and
scatter.
A part of the scattering deposits 10 may move toward the surface of
the wafer W along the peripheral portion thereof. Since, however,
the shielding plate 89 is provided, the scattering substances are
blocked or bounced by the shielding plate 89 and moved toward the
outer side of the wafer W.
Further, the second vacuum chamber 41 is vacuum-evacuated through
the gas exhaust port 45 formed at the bottom portion, so that the
scattering substances are moved toward the gas exhaust port 45.
Hence, the deposits 10 peeled from the peripheral portion of the
wafer W are prevented from being re-adhered to the surface of the
wafer W.
The first nozzle unit 6 and the second nozzle unit 90 are installed
such that the gas clusters are ejected from different positions
onto the wafer W along the circumferential direction and do not
interfere with each other in the case of ejecting the gas clusters
from the first nozzle unit 6 and the second nozzle unit 90
simultaneously. The gas clusters may be ejected from the first
nozzle unit 6 and the second nozzle unit 90 at different timings.
For example, after rotating the wafer W by 360.degree. while a gas
cluster is ejected from the second nozzle unit 90, the ejection
from the second nozzle unit 90 is stopped and a gas cluster is
ejected from the first nozzle unit 6 while the wafer W is rotated
by 360.degree..
Both of the purge gas nozzle 80 of the first embodiment and the
shielding plate 89 of the second embodiment may be employed so that
the present invention can realize both of the effect of moving the
deposit peeled from the peripheral portion of the wafer W to the
outer side of the wafer W by the purge gas and the effect of
preventing the deposit from moving toward the surface of the wafer
W by the shielding plate 89.
TEST EXAMPLES
Test Example 1
A pattern group was formed on a surface of a bare silicon wafer. As
shown in FIG. 13, the pattern group includes rectangular
polysilicon patterns arranged in a zigzag shape and spaced apart
from each other at an interval "a" of 500 nm in a width direction,
each pattern having a height "h" of 100 nm, a width "d" of 45 nm
and a length L of 600 nm. The nozzle unit 6 was provided
immediately above the pattern group so that the axis thereof is
perpendicular to the surface of the wafer W. A gas cluster of
CO.sub.2 was ejected from the nozzle unit 6 to the pattern group. A
distance between the orifice of the nozzle unit 6 and the pattern
group (the wafer surface) was 1 cm. A temperature in the nozzle
unit 6 was set to 20.degree. C. A pressure was varied to 3 MPa, 4
MPa and 5 MPa.
FIGS. 14 to 16 illustrate SEM images showing the state of the
pattern group after the ejection of the gas cluster at the
respective pressures. When the pressure in the nozzle unit 6
(pressure on the primary side of the orifice) was 3 MPa, the
pattern did not collapse. When the pressure was 4 MPa, the tilt
ratio of the pattern was 5% and the pattern hardly collapsed. When
the pressure was 5 MPa, the tilt ratio of the pattern was 100%.
FIG. 17 shows relation between the pressure in the nozzle unit 6
and the tilt ratio of the pattern. It is clear from the result that
the tilt ratio of the pattern is considerably increased as the
pressure of CO.sub.2 gas becomes closer to the pressure on the
gas-liquid boundary line. Therefore, as described above, the
pressure at which a firm gas cluster is obtained, i.e., the
pressure slightly lower than the pressure on the vapor pressure
line at a temperature of CO.sub.2 gas of the present invention, is
determined by monitoring the state of the pattern in the case of
ejecting the gas cluster to the pattern, for example.
Test Example 2
In order to evaluate the present invention, the following test was
conducted by using the substrate cleaning method in accordance with
the above-described embodiment.
First, a resist film that is an organic film was formed on the
wafer W. Then, the wafer W was etched by a plasma. Next, the state
of the peripheral portion of the wafer W in the case of ejecting a
CO.sub.2 cluster to the backside (peripheral portion) of the wafer
W (diameter 30 cm) (test example) was compared with the state of
the peripheral portion of the wafer W in the case of ejecting no
CO.sub.2 cluster thereto (comparative example).
The CO.sub.2 gas was supplied into the nozzle unit 6 at a pressure
of 5 MPa under the atmospheric temperature of 20.degree. C. A
pressure in the second vacuum chamber 41 was set to 30 Pa. The gas
cluster was ejected to the wafer W at an angle of 90.degree.. FIG.
18 shows a result of monitoring the SEM images of portions P1 to P6
of the peripheral portion of the wafer W in the test example and
the comparative example. P1 and P2 were set to backside portions of
the wafer W. P3 and P4 were set to beveled portions. P5 and P6 were
set to side surface portions.
In the wafer W of the comparative example, the deposit was adhered
to the beveled portions P3 and P4 or the side surface portions P5
and P6 with a thickness of about 300 nm.
The deposit was also monitored at the backside portions P1 and P2.
On the other hand, in the wafer W of the test example, the deposit
was not adhered to the backside portions P1 and P2 and hardly
remained at the beveled portions P3 and P4 and the side surface
portions P5 and P6. From the above, it is clear that the deposit is
easily adhered to the beveled portion or the side surface portion
of the wafer W and the deposit adhered to the peripheral portion of
the wafer W can be reliably removed by the substrate cleaning
method of the present invention.
* * * * *